Controlled Release Fertilizer And Method For Production Thereof

ABSTRACT

A controlled release fertilizer material comprising a particulate plant nutrient surrounded by a coating which is the reaction product of a mixture comprising: a polyol, an isocyanate and an organic wax.

This is a continuation application of application Ser. No. 10/659,432,filed Sep. 11, 2003, which is a continuation of application Ser. No.09/604,161, filed Jun. 27, 2000, now U.S. Pat. No. 6,663,686, issuedDec. 16, 2003, the contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a controlled release fertilizer and toa method for production thereof.

2. Description of the Prior Art

Fertilizers have been used for many years to supplement nutrients ingrowing media.

In recent years the art has focused on techniques to deliver controlledamounts of plant nutrients to the soil or other growing media. This hasbeen done so that, on one hand, the growing plants are not adverselydeprived of nutrients and, on the other hand, an over supply ofnutrients is avoided. An over supply of nutrients can result in toxicityto the plants or losses from leaching. The resulting improvement in FUE(fertilizer use efficiency) can reduce the rate and the frequency ofnutrient application.

U.S. Pat. No. 5,538,531 [Hudson et al. (Hudson)] and the prior art citedtherein provides a useful overview of methods of conveying controlledrelease properties to a particulate plant nutrient. Specifically, Hudsonteaches a controlled release, particulate fertilizer product having awater soluble fertilizer central mass encased in a plurality of waterinsoluble, abrasion resistant coatings. At least one inner coating is aurethane reaction product derived from recited isocyanates and polyols.The outer coating is formed from an organic wax having a drop meltingpoint in the range of from 50° C. to 120° C. The general teachings ofHudson and those of the Examples in Hudson make it clear that the Hudsonprocess involves curing the urethane coating(s) around the particulateplant nutrient and, thereafter, applying to the cured urethanecoating(s) the outer layer of organic wax.

It is also known in the art to pre-coat particulate plant nutrient withan organic wax or similar material as a means to regular or otherwiseimprove the surface of the particulate plant nutrient prior to coatingthereof with the urethane forming reagents.

Despite these advances in the art, there is still room for improvement.Specifically, it would be desirable to have a controlled releasefertilizer and process for production thereof which would allow for theready customization of the release rate profile of a given particulateplant nutrient having applied thereto a given amount of urethanecoating(s). It would also be desirable to be able to achieve a desirablerelease rate profile for a given particulate plant nutrient usingsignificantly reduced amounts of coating materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a novel controlledrelease fertilizer which obviates or mitigates at least one of theabove-mentioned disadvantages of the prior art.

Accordingly, in one of its aspects the present invention provides acontrolled release fertilizer material comprising a particulate plantnutrient surrounded by a coating which is the reaction product of amixture comprising: a polyol, an isocyanate and an organic wax.

In another of its aspects, the present invention provides a process forproducing a controlled release fertilizer material comprising the stepsof:

(a) contacting a particulate plant nutrient with a mixture comprising: apolyol, an isocyanate and an organic wax to produce a coatingsurrounding the particulate plant nutrient; and

(b) curing the coating to produce the controlled release fertilizermaterial.

Thus, we have surprisingly and unexpectedly discovered that an improvedcontrolled release fertilizer material and process for productionthereof may be achieved from a coating which is the reaction product ofa mixture comprising: a polyol, an isocyanate and an organic wax.Specifically, while it is known use wax as a pre-coat before applicationof the urethane layer and/or as post-coat after application of theurethane layer, the advantages of incorporating the wax with theurethane forming reagents has heretofore been unknown. This advantagesinclude:

-   -   (i) the ability to extend the release rate profile for a give        plant nutrient having a given amount of urethane coating        thereon;    -   (ii) the ability to achieve a desirable release rate profile        using significantly less coating that used with comparable prior        art coating techniques; and    -   (iii) the ability to obtain such a product via one-step process        (i.e., compared to the multi-step processes of the prior art).        Other advantages will become apparent to those of skill in art        having the present specification in hand.

BRIEF DESCRIPTION OF THE DRAWING

Embodiments of the present invention will be described with reference tothe accompanying FIGURE in which there is illustrated the release rateprofile a controlled release fertilizer in accordance with the presentinvention and the release rate profiles of prior art controlled releasefertilizers.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Accordingly, in one of its aspects, the present invention relates to acontrolled release fertilizer material comprising a particulate plantnutrient surrounded by a coating.

The choice of particulate plant nutrient material useful for the presentcontrolled release fertilizer material is not particularly restrictedand is within the purview of a person skilled in the art.

For example, the plant nutrient material used may selected from thosedisclosed in Hudson. Preferably, such a plant nutrient comprises a watersoluble compound, more preferably a compound containing at least onemember selected from the group consisting of nitrogen, phosphorus,potassium, sulfur and mixtures thereof. A preferred such plant nutrientcomprises urea. Other useful examples of plant nutrients are taught inU.S. Pat. No. 5,571,303 [Bexton]—e.g., ammonium sulfate, ammoniumphosphate and mixtures thereof.

Preferably, the coating surrounds the plant nutrient material in anamount in the range of from about 1.0 to about 10 percent by weight,more preferably from about 1.5 to about 5.0 percent by weight, mostpreferably from about 2.0 to about 4.0 percent by weight, based on theweight of the plant nutrient material.

The coating is the reaction product of a mixture comprising: a polyol,an isocyanate and an organic wax.

The choice of polyol is not particularly restricted and is within thepurview of a person skilled in the art. For example, the polyol may be ahydroxyl-terminated backbone of a member selected from the groupcomprising polyether, polyester, polycarbonate, polydiene andpolycaprolactone. Preferably, such a polyol is selected from the groupcomprising hydroxyl-terminated polyhydrocarbons, hydroxyl-terminatedpolyformals, fatty acid triglycerides, hydroxyl-terminated polyesters,hydroxymethyl-terminated polyesters, hydroxymethyl-terminatedperfluoromethylenes, polyalkyleneether glycols, polyalkylenearyleneetherglycols and polyalkyleneether triols. More preferred polyols areselected from the group comprising polyethylene glycols, adipicacid-ethylene glycol polyester, poly(butylene glycol), poly(propyleneglycol) and hydroxyl-terminated polybutadiene—see, for example, Britishpatent No. 1,482,213. The most preferred such polyol is a polyetherpolyol. Preferably, such a polyether polyol has a molecular weight inthe range of from about 200 to about 20,000, more preferably from about2,000 to about 10,000, most preferably from about 2,000 to about 8,000.

A particularly preferred class of polyols are those disclosed in Hudson.Preferably, such a polyol comprises from about 2 to about 6 hydroxylmoieties. More preferably, such a polyol comprises at least one C₁₀-C₂₂aliphatic moiety. Most preferably, the polyol comprises castor oil.

Additionally, the polyol may be derived from natural sources such assoybean, corn, canola and the like (i.e., to produce naturally occurringmodified oils). An example of such a synthetic polyol comprising acanola base is commercially available from Urethane Soy Systems Corp.(Princeton, Ill.).

The isocyanate suitable for used in producing the coating is notparticularly restricted and the choice thereof is within the purview ofa person skilled in the art. Generally, the isocyanate compound suitablefor use may be represented by the general formula:

Q(NCO)_(i)

wherein i is an integer of two or more and Q is an organic radicalhaving the valence of i. Q may be a substituted or unsubstitutedhydrocarbon group (e.g. an alkylene or arylene group). Moreover, Q maybe represented by the general formula:

Q¹-Z-Q¹

wherein Q¹ is an alkylene or arylene group and Z is chosen from thegroup comprising —O—, —O-Q¹-, —CO—, —S—, —S-Q¹-S— and —SO₂—. Examples ofisocyanate compounds which fall within the scope of this definitioninclude hexamethylene diisocyanate, 1,8-diisocyanato-p-methane, xylyldiisocyanate, (OCNCH₂CH₂CH₂OCH₂O)₂,1-methyl-2,4-diisocyanatocyclohexane, phenylene diisocyanates, tolylenediisocyanates, chlorophenylene diisocyanates,diphenylmethane-4,4′-diisocyanate, naphthalene-1,5-diisocyanate,triphenylmethane-4,4′,4″-triisocyanate andisopropylbenzene-alpha-4-diisocyanate.

In another embodiment, Q may also represent a polyurethane radicalhaving a valence of i. In this case Q(NCO)_(i) is a compound which iscommonly referred to in the art as a prepolymer. Generally, a prepolymermay be prepared by reacting a stoichiometric excess of an isocyanatecompound (as discussed hereinabove) with an active hydrogen-containingcompound (as discussed hereinabove), preferably thepolyhydroxyl-containing materials or polyols discussed above. In thisembodiment, the polyisocyanate may be, for example, used in proportionsof from about 30 percent to about 200 percent stoichiometric excess withrespect to the proportion of hydroxyl in the polyol.

In another embodiment, the isocyanate compound suitable for use in theprocess of the present invention may be selected from dimers and trimersof isocyanates and diisocyanates, and from polymeric diisocyanateshaving the general formula:

[Q″(NCO)_(i)]_(j)

wherein both i and j are integers having a value of 2 or more, and Q″ isa polyfunctional organic radical, and/or, as additional components inthe reaction mixture, compounds having the general formula:

L(NCO)_(i)

wherein i is an integer having a value of 1 or more and L is amonofunctional or polyfunctional atom or radical. Examples of isocyanatecompounds which fall with the scope of this definition includeethylphosphonic diisocyanate, phenylphosphonic diisocyanate, compoundswhich contain a ═Si—NCO group, isocyanate compounds derived fromsulphonamides (QSO₂NCO), cyanic acid and thiocyanic acid.

See also, for example, British patent No. 1,453,258.

Non-limiting examples of suitable isocyanates include: 1,6-hexamethylenediisocyanate, 1,4-butylene diisocyanate, furfurylidene diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,4′-diphenylmethanediisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenylpropanediisocyanate, 4,4′-diphenyl-3,3′-dimethyl methane diisocyanate,1,5-naphthalene diisocyanate, 1-methyl-2,4-diisocyanate-5-chlorobenzene,2,4-diisocyanato-s-triazine, 1-methyl-2,4-diisocyanato cyclohexane,p-phenylene diisocyanate, m-phenylene diisocyanate, 1,4-naphthalenediisocyanate, dianisidine diisocyanate, bitoluene diisocyanate,1,4-xylylene diisocyanate, 1,3-xylylene diisocyanate,bis-(4-isocyanatophenyl)methane,bis-(3-methyl-4-isocyanatophenyl)methane, polymethylene polyphenylpolyisocyanates and mixtures thereof.

A particularly preferred group of isocyanates are those described inHudson.

Preferably, the polyol and isocyanate are used in amounts such that theratio of NCO groups in the isocyanate to the hydroxyl groups in thepolyol is in the range of from about 0.8 to about 3.0, more preferablyfrom about 0.8 to about 2.0, most preferably from about 0.9 to about1.1.

The wax used in the mixture to produce the coating may be selected fromthose described in Hudson and from silicon waxes (commercially availablefrom Dow Corning). Thus, the preferred wax comprises a drop meltingpoint in the range of from about 50° C. to about 120° C. Morepreferably, the wax is substantially non-tacky below a temperature ofabout 40° C. Most preferably, the wax comprises a C₃₀₊ alpha olefin.

Preferably, the organic wax is present in the mixture in an amount of upto about 50 percent by weight, based on the combined weight of theorganic wax and the polyol. More preferably, the organic wax is presentin the mixture in an amount in the range of from about 1.0 to about 25percent by weight, based on the combined weight of the organic wax andthe polyol. Most preferably, the organic was is present in the mixturein an amount in the range of from about 2.0 to about 10 percent byweight based, on the combined weight of the organic wax and the polyol.

Step (a) in the present process comprises contacting a particulate plantnutrient with a mixture comprising: a polyol, an isocyanate and anorganic wax to produce a coating surrounding the particulate plantnutrient. The precise mode of applying the mixture to the plant nutrientis not particularly restricted—see for, example column 5, lines 31-63 ofHudson.

In the present process, it is preferred to conduct Step (a) at atemperature in the range of from about 50° C. to about 105° C., morepreferably in the range of from about 60° C. to about 90° C., mostpreferably in the range of from about 70° C. to about 80° C.

Preferably, Step (a) comprises contacting the particulate plant nutrientwith a first stream comprising the polyol and a second stream comprisingthe isocyanate, the first stream and the second stream being independentof one another. More preferably, the first stream comprises a mixture ofthe polyol and the organic wax. In this embodiment, the particulateplant nutrient may be contacted simultaneously with the first stream andthe second stream. Alternatively, the particulate plant nutrient withthe first stream followed by the second stream. In a further preferredembodiment, Steps (a) and (b) of the present process are repeated atleast once to produce a controlled release fertilizer material having aplurality of coating layers.

Embodiments of the present invention will be illustrated with referenceto the following Examples which should not be used to limit or construethe invention.

Example 1

In this Example, a controlled release fertilizer material was preparedaccording to the teachings of U.S. Pat. No. 5,538,531 [Hudson et al.(Hudson)]. Accordingly, it will be recognized that this Example isprovided for comparative purposes only and is outside the scope of thepresent invention.

The apparatus used in this Example was capable of applying coatingcomponents to a 7.5 kg batch. The apparatus consisted of a Plexiglashorizontal drum 16 inches in diameter and 20 inches in length. The drumend plates had a central 5 inch hole through which the coatingcomponents and the substrate are added. The drum internals consisted offour substantially evenly spaced longitudinal baffles, each baffle beingabout 1 inch in height. The drum was rotated at 75 fpm peripheral speedor about 18 rpm using a Separ™, variable speed drive, horizontal drumroller. The internal temperature of the drum and substrate wasmaintained at about 75° C. using variable setting electric heating guns.The heating guns were positioned to direct hot air through the holes inthe drum end plates.

The coating components were added at a substantially consistent rateusing individual Masterflex™ peristaltic pumps and a modified Amacoil™Machinery auto-sampler. The sampler portion was removed and anindividual stainless steel tubing for each component was attached to thedrive assembly. This allowed the coating components to be distributedthe full length of the drum at a substantially constant travel speed.

The substrate used in this Example was granulated urea (46-0-0). Thissubstrate had a SGN (Size Guide Number) of 240. The substrate (7.5 kg)was preheated in an oven to about 75° C. and was allowed to roll in thecoating drum until the temperature has stabilized to 75° C.

The polyol used in this Example was commercially available castor oil inan amount of 42.95 g. The isocyanate used in this Example was polymericdiphenylmethane diisocyanate (BASF PAPI No. 17) in an amount of 19.52 g.The two components are simultaneously added to the coating apparatusthrough individual lines or pipettes near the top of the rolling bed.The 2.5 weight percent coat was applied to the substrate in threesubstantially equal layers with about six minutes between application ifeach layer—i.e., the weight of the total coat was 2.5 weight percentbased on the weight of the substrate.

A C₃₀₊ alpha olefin wax commercially available from Chevron waspre-heated to about 150° C. and then was applied in a single layer tothe urethane coated substrate. The wax was used in an amount to providea weight of 1.5 weight percent based on the weight of the substrate. Sixminutes after the wax was applied, the drum and contents are cooled witha controlled stream of pressurized air to about 35° C.

Thus, in this Example, the sum of the urethane coat and the wax layerwas 4 weight percent based on the weight of the substrate.

The water release rate profile for the controlled release fertilizermaterial was then determined. In the analysis, a Technicon AutoAnalyzer™was calibrated and used pursuant to the teachings of AutomatedDetermination of Urea and Ammoniacal Nitrogen (University of Missouri,1980). The following procedure was used:

-   -   1. Accurately weigh 15 grams (+0.1 mg) of the sample into a        weigh dish. Record the weight of sample. Transfer the sample to        125 mL Erlenmeyer flask.    -   2. Add 75 mL of demineralized water and stopper the flask.    -   3. Gently swirl the sample and water until all the particles are        submersed.    -   4. Let the sample stand for a specified time at a constant        temperature (typically at room temperature).    -   5. Gently swirl the flask to mix the solution and decant only        the solution to a 100 mL volumetric flask.    -   6. Rinse the sample with demineralized water adding to the        volumetric flask.    -   7. Bulk to volume of volumetric flask and mix thoroughly.    -   8. If the test is to be repeated for another time period, repeat        starting at Step 2.    -   9. Once the Technicon AutoAnalyzer II is on line, transfer some        of this solution (or perform the required dilutions if        necessary) to the Technicon sample cups for analysis.    -   10. Record the results as parts per million N—NH₃ (read directly        from a Shimadzu Integrator).

Example 2

The methodology in Example 1 was repeated with the exception that, priorto application of the urethane forming polyol and isocyanate, thesubstrate was pre-coated with the C₃₀₊ alpha olefin wax (pre-heated toabout 150° C.) applied as a single layer. The wax was used in an amountto provide a weight of 0.3 weight percent based on the weight of thesubstrate. Accordingly, it will be recognized that this Example isprovided for comparative purposes only and is outside the scope of thepresent invention.

A three-layer polyurethane coating as applied to the pre-coatedsubstrate as described in Example 1 (44.0 g castor oil and 18.4 gisocyanate). Again, the weight of the total polyurethane coat was 2.5weight percent based on the weight of the substrate. A 600 g portion ofthe urethane coated substrate was removed.

Thereafter, a three-layer coating of the C₃₀₊ alpha olefin wax(pre-heated to about 150° C.) was applied to the remaining urethanecoated substrate. The wax was used in an amount to provide a weight of1.5 weight percent based on the weight of the substrate (in this case,about 35 g was per layer of the three-layer coating).

The water release rate profile for the controlled release fertilizermaterial was then determined using the test procedure described above inExample 1.

Example 3

In this Example, a controlled release fertilizer was prepared inaccordance with the present invention.

The apparatus used to apply the coating components was a SS horizontalinsulated drum having a 12 inch diameter a 5½ inches in width. Anenclosed back plate was attached to a variable speed drive. The frontplate had a central 8 inch opening through which the substrate and thecoating components are added. The drum internals consist of foursubstantially evenly spaced longitudinal baffles, each about ½ inchhigh. The drum was rotated at 75 fpm peripheral speed or about 24 rpm.The internal temperature of the drum and substrate was maintained atabout 75° C. using a variable setting electric heating gun. The coatingcomponents are added using individual automatic macro pipettes capableof adding ⅓ the weight of each coating component in a single addition.

The same substrate (1 kg) as used in Examples 1 and 2 was pre-heated to75° C. in the (smaller) apparatus described above. Castor oil (5.63 g)at 140° C. was mixed with C₃₀₊ alpha olefin wax (0.33 g). A coating wasapplied to the substrate consisting of three layers of 5.96 g (5.5 wt. %C₃₀₊ in castor oil) of the castor oil/wax mixture and 2.35 g isocyanateadded simultaneously for a total coating weight of 2.5%. The time periodbetween application of successive layers of urethane was approximately 6minutes. Six minutes after the final urethane layer was applied theproduct was cooled.

The water release rate profile for the controlled release fertilizermaterial was then determined using the test procedure described above inExample 1.

The water release rate profiles for the controlled release fertilizermaterial produced in Examples 1-3 are illustrated in the accompanyingFIGURE.

As shown, when it is desired to have material with a release profile ofnitrogen extending over 6-8 months, the water release rate profile forthe material produced in Example 3 (the invention) is significantlybetter than that for the material produced in Example 1 (the Hudsonmaterial). Further, this was achieved using significantly less coatingin Example 3 (2.5 weight percent based on the weight of the substrate)compared with Example 1 (4.0 weight percent based on the weight of thesubstrate).

With reference to Example 2 (wax pre-coat and post-coat), while thewater release rate profile is closer to that achieved in Example 3 (theinvention), this was achieved using a three-step process whereas thematerial of Example 3 was made using a one-step process.

Accordingly, the material of Example 3 and the production thereof is asignificant advance over the prior art.

While the present invention has been described in detail, includingreference to the Examples, it will of course be readily understood thata number of modifications to the exemplified embodiment will be apparentto those of skill in the art with this specification in hand, whichmodifications do not depart from the spirit and scope of the presentinvention.

All publications, patents and patent applications referred to herein areincorporated by reference in their entirety to the same extent as ifeach individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by referencein its entirety.

1. A controlled release fertilizer material comprising a particulateplant nutrient surrounded by a coating which is the reaction product ofa mixture comprising: a polyol, an isocyanate and an organic wax.
 2. Thecontrolled release fertilizer material defined in claim 1, wherein theplant nutrient comprises a water soluble compound.
 3. The controlledrelease fertilizer material defined in claim 2, wherein the watersoluble compound comprises a compound containing at least one memberselected from the group consisting of nitrogen, phosphorus, potassium,sulfur and mixtures thereof.
 4. The controlled release fertilizermaterial defined in claim 1, wherein the plant nutrient comprises urea.5. The controlled release fertilizer material defined in claim 1,wherein the polyol comprises from about 2 to about 6 hydroxyl moieties.6. The controlled release fertilizer material defined in claim 1,wherein the polyol comprises at least one C₁₀-C₂₂ aliphatic moiety. 7.The controlled release fertilizer material defined in claim 1, whereinthe polyol comprises castor oil.
 8. The controlled release fertilizermaterial defined in claim 1, wherein the isocyanate is selected from thegroup consisting of diphenylmethane diisocyanate, toluene diisocyanate,aliphatic isocyantes, derivatives thereof, polymers thereof and mixturesthereof.
 9. The controlled release fertilizer material defined in claim1, wherein the isocyanate contains from about 1.5 to about 3.0isocyanate groups per molecule.
 10. The controlled release fertilizermaterial defined in claim 1, wherein the isocyanate contains from about10% to about 50% NCO.
 11. The controlled release fertilizer materialdefined in claim 1, wherein the isocyanate comprises polymericdiphenylmethane diisocyanate.
 12. The controlled release fertilizermaterial defined in claim 1, wherein the organic wax comprises a dropmelting point in the range of from about 50° C. to about 120° C.
 13. Thecontrolled release fertilizer material defined in claim 1, wherein theorganic wax is substantially non-tacky below a temperature of about 40°C.
 14. The controlled release fertilizer material defined in claim 1,wherein organic wax comprises a C₃₀₊ alpha olefin.
 15. The controlledrelease fertilizer material defined in claim 1, wherein the coating ispresent in an amount in the range of from about 1 to about 10 percent byweight based on the weight of particulate plant nutrient.
 16. Thecontrolled release fertilizer material defined in claim 1, wherein thecoating is present in an amount in the range of from about 1.5 to about5.0 percent by weight based on the weight of particulate plant nutrient.17. The controlled release fertilizer material defined in claim 1,wherein the coating is present in an amount in the range of from about2.0 to about 4.0 percent by weight based on the weight of particulateplant nutrient.
 18. The controlled release fertilizer material definedin claim 1, wherein the ratio of NCO groups from the isocyanate to thehydroxyl groups in the polyol in the mixture is in the range of fromabout 0.8 to about 3.0.
 19. The controlled release fertilizer materialdefined in claim 1, wherein the ratio of NCO groups from the isocyanateto the hydroxyl groups in the polyol in the mixture is in the range offrom about 0.8 to about 2.0.
 20. The controlled release fertilizermaterial defined in claim 1, wherein the ratio of NCO groups from theisocyanate to the hydroxyl groups in the polyol in the mixture is in therange of from about 0.9 to about 1.1.
 21. The controlled releasefertilizer material defined in claim 1, wherein the amount of organicwax in the mixture is up to about 50 percent by weight based on thecombined weight of the organic wax and the polyol.
 22. The controlledrelease fertilizer material defined in claim 1, wherein the amount oforganic wax in the mixture is in the range of from about 1.0 to about 25percent by weight based on the combined weight of the organic wax andthe polyol.
 23. The controlled release fertilizer material defined inclaim 1, wherein the amount of organic wax in the mixture is in therange of from about 2.0 to about 10 percent by weight based on thecombined weight of the organic wax and the polyol.
 24. A process forproducing a controlled release fertilizer material comprising the stepsof: (a) contacting a particulate plant nutrient with a mixturecomprising: a polyol, an isocyanate and an organic wax to produce acoating surrounding the particulate plant nutrient; and (b) curing thecoating to produce the controlled release fertilizer material.
 25. Theprocess defined in claim 24, wherein the particulate material isagitated during Step (a).
 26. The process defined in claim 24, whereinStep (a) is conducted at a temperature in the range of from about 50° C.to about 105° C.
 27. The process defined in claim 24, wherein Step (a)is conducted at a temperature in the range of from about 60° C. to about90° C.
 28. The process defined in claim 24, wherein Step (a) isconducted at a temperature in the range of from about 70° C. to about80° C.
 29. The process defined in claim 24, wherein Step (a) comprisescontacting the particulate plant nutrient with a first stream comprisingthe polyol and a second stream comprising the isocyanate, the firststream and the second stream being independent of one another.
 30. Theprocess defined in claim 29, wherein the first stream comprises amixture of the polyol and the organic wax.
 31. The process defined inclaim 29, wherein Step (a) comprises contacting the particulate plantnutrient simultaneously with the first stream and the second stream. 32.The process defined in claim 29, wherein Step (a) comprises contactingthe particulate plant nutrient with the first stream followed by thesecond stream.
 33. The process defined in claim 24, wherein Steps (a)and (b) are repeated at least once to produce a controlled releasefertilizer material having a plurality of coating layers.
 34. Theprocess defined in claim 24, wherein the plant nutrient comprises awater soluble compound.
 35. The process defined in claim 34, wherein thewater soluble compound comprises a compound containing at least onemember selected from the group consisting of nitrogen, phosphorus,potassium, sulfur and mixtures thereof.
 36. The process defined in claim24, wherein the plant nutrient comprises urea.
 37. The process definedin claim 24, wherein the polyol comprises from about 2 to about 6hydroxyl moieties.
 38. The process defined in claim 24, wherein thepolyol comprises at least one C₁₀-C₂₂ aliphatic moiety.
 39. The processdefined in claim 24, wherein the polyol comprises castor oil.
 40. Theprocess defined in claim 24, wherein the isocyanate is selected from thegroup consisting of diphenylmethane diisocyanate, toluene diisocyanate,aliphatic isocyanates derivatives thereof, polymers thereof and mixturesthereof.
 41. The process defined in claim 24, wherein the isocyanatecontains from about 1.5 to about 3.0 isocyanate groups per molecule. 42.The process defined in claim 24, wherein the isocyanate contains fromabout 10% to about 50% NCO.
 43. The process defined in claim 24, whereinthe isocyanate comprises polymeric diphenylmethane diisocyanate.
 44. Theprocess defined in claim 24, wherein the organic wax comprises a dropmelting point in the range of from about 50° C. to about 120° C.
 45. Theprocess defined in claim 24, wherein the organic wax is substantiallynon-tacky below a temperature of about 40° C.
 46. The process defined inclaim 24, wherein organic wax comprises a C₃₀₊ alpha olefin.
 47. Theprocess defined in claim 24, wherein the mixture is used in an amount toprovide a coating in an amount in the range of from about 1 to about 10percent by weight based on the weight of particulate plant nutrient. 48.The process defined in claim 24, wherein the mixture is used in anamount to provide a coating in an amount in the range of from about 1.5to about 5.0 percent by weight based on the weight of particulate plantnutrient.
 49. The process defined in claim 24, wherein the mixture isused in an amount to provide a coating in an amount in the range of fromabout 2.0 to about 4.0 percent by weight based on the weight ofparticulate plant nutrient.
 50. The process defined in claim 24, whereinthe ratio of NCO groups from the isocyanate to the hydroxyl groups inthe polyol in the mixture is in the range of from about 0.8 to about3.0.
 51. The process defined in claim 24, wherein the ratio of NCOgroups from the isocyanate to the hydroxyl groups in the polyol in themixture is in the range of from about 0.8 to about 2.0.
 52. The processdefined in claim 24, wherein the ratio of NCO groups from the isocyanateto the hydroxyl groups in the polyol in the mixture is in the range offrom about 0.9 to about 1.1.
 53. The process defined in claim 24,wherein the amount of organic wax in the mixture is up to about 50percent by weight based on the combined weight of the organic wax andthe polyol.
 54. The process defined in claim 24, wherein the amount oforganic wax in the mixture is in the range of from about 1.0 to about 25percent by weight based on the combined weight of the organic wax andthe polyol.
 55. The process defined in claim 24, wherein the amount oforganic wax in the mixture is in the range of from about 2.0 to about 10percent by weight based on the combined weight of the organic wax andthe polyol.
 56. A controlled release fertilizer material comprising aparticulate plant nutrient surrounded by a coating which is the reactionproduct of a mixture comprising: a polyol, an isocyanate and an organicwax, wherein the polyol comprises at least one C₁₀-C₂₂ aliphatic moiety.57. A process for producing a controlled release fertilizer materialcomprising the steps of: (a) contacting a particulate plant nutrientwith a mixture comprising: a polyol, an isocyanate and an organic wax toproduce a coating surrounding the particulate plant nutrient, whereinthe polyol comprises at least one C₁₀-C₂₂ aliphatic moiety; and (b)curing the coating to produce the controlled release fertilizermaterial.